1. Technical Field of the Invention
The present invention relates generally to earth boring bits, and more particularly to a rotary drag bit mounted with a straight or spiral bladed segment impregnated with diamond for drilling a variety of types of rock.
2. Description of Related Art
Impregnated drill bits typically employ a cutting face composed of superabrasive cutting particles, such as natural or synthetic diamond grit, dispersed within a matrix of wear-resistant material. As such a drill bit is operated to drill a formation, the matrix and embedded diamond particles wear, worn cutting particles are lost and new cutting particles are exposed. These diamond particles may either be natural or synthetic and may be cast integral with the body of the bit, as in low-pressure infiltration, or may be preformed separately, as in hot isostatic pressure infiltration, and attached to the bit by brazing or furnaced to the bit body during the manufacturing by an infiltration process.
Reference is now made to FIG. 1 which shows a prior art impregnated bit. This bit is made with aggregate of diamond and matrix powder which is infiltrated. The diamond particles are cast within a supporting material to form an abrasive layer. During operation of the drill bit, diamonds within the abrasive layer are gradually exposed as the supporting material is worn away. A limitation of this bit concerns the impossibility to customize the wear rate because of the homogeneous distribution of the diamond within the abrasive layer. Reference is made to U.S. Pat. No. 6,095,265, the disclosure of which is hereby incorporated by reference, which provides a solution to this issue.
In the late 1990's, new designs were introduced which were based on the use of discrete segment impregnated cutting structures extending upwardly from abrasive particulate-impregnated blades defining a plurality of fluid passages between on the bit face. FIG. 2 shows an example of a prior art use of bladed segments mounted on straight blade cutting structures.
FIG. 3 shows an example of a prior art use of discrete segments mounted on a spiral cutting structure.
Reference is further made to: “Impregnated Rotary Drag Bit”, U.S. Pat. No. 6,843,333; “Laminated and Composite Impregnated Cutting Structures for Drill Bits”, U.S. Pat. No. 6,742,611; and “Impregnated Bit with PDC Cutters in Cone Area”, U.S. Pat. No. 6,510,906, the disclosures of all of which being incorporated by reference herein.